Telephone repeater



July 27, w54 G. H. BRoDlE Re. 23,854

TELEPHONE REPEATER Original Filed Dec. 13, 1946 sheets-Sheet 1 INVENTOR.'

GEORGE H. BRODIE www ATTORNEY July 27, 1954 G. H. BRoDlE Re. 23,854

TELEPHONE REPEATER Original Filed Dec. l5, 1946 5 Sheets-Sheet 2 GEORGE H. BROD IE BY du/f ATTORNEY 3 SheenS-Sheet 5 Original Filed Dec. 15, 1946 @www @www

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INVENTOR:

GEORGE H. BRODIE ATTORNEY Reissued July 27, 1954 TELEPHONE REPEATER.

George H. Brodie, La Grange, Ill., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Original No. 2,615,997, dated October 2.8, 1952,

Serial No. 716,654, December 13, 1946. Application for reissue October 28, 1953, Serial No.

13 Claims.

This invention relates to telephone repeaters. Its principal object is the provision of a new and improved two-way telephone repeater so arranged 'that simple two-winding repeating coils may be employed to interconnect it with the two line sections between which it is to repeat, and to interconnect it with the bala-nce networks associated with such line sections.

As is well known, a long two-way telephone line is severed at one or more desired points, and a twoway telephone repeater is inserted between the two sections oi the line at each such point to amplify the attenuated voice currents to the desired extent. Such a repeater contains a separate amplifying channel for each oi the two directions of conversation. in order to prevent the amplied voice currents passing through the repeater in one direction from being returned, amplified, to the initial line section by way of the other channel, it is common practice to employ a balance network for each line section, and to employ a so-called hybrid coil to join each line section and associated balance network with the two channels ci the repeater. Such a coil commonly has five separate windings including four which must be nicely balanced amongst themselves, in that they are connected in series between the line section and the balance network in order to provide a pair oi connections representing the neutral points of these windings. These so-called hybrid coils have generally proven to be quite expensive to produce, because of the large number of windings which must be maintained in substantial balance. Alternative arrangements have been tried with some success, including the use of two or more interconnected repeating coils to replace a hybrid coil, but all such arrangements have generally been found to be open to the objection that they do not provide the desired economy of production. The present invention obviates the foregoing difficulties by providing a two-way telephone repeater which employs two pairs of simple two-winding repeating coils serving within the repeater arrangement to prevent the undesired local signal circulation referred to as singing so long as the respective two-winding repeating coils of each pair are substantial equivalents of each other.

An outstanding feature of the invention relates to the arrangement included in each channel for amplifying and repeating voice currents, incoming over a line section, equally to the opposite line section and to the balance network associated therewith, and for insuring that the re- Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates additions made by reissue.

sulting voice currents flowing from the last named section baci: toward the original section are canceled by an equal and opposite flow arising from the amplified and repeated voice currents transmitted to the concerned balance network. In accordance with this feature, a phase inverter, consisting preferably of a vacuum-tube amplifier adjusted for zero amplification, is employed in one of two opposed paths to invert the phase oi the amplified Voice currents returned thereover.

Other objects and features of the invention, subordinate for the most part to the foregoing, will appear upon a further perusal of the description.

The accompanying drawings, comprising Figs. l to o, show in circuit diagram, and in block diagram, a preferred embodiment of the invention and desirable modiiications thereof:

Fig. i is a circuit diagram of a two-way repeater embodying the invention in its preferred form;

Fig. 2 is a similar diagram of a two-way repeater embodying the invention in one modified form;

Fig. 3 is a block diagram of the repeater apparatus of Fig. 1;

Fig. 4 is a block diagram of the repeater apparatus of Fig. 2; and

Figs. 5 and 6 are block diagrams of further modifications.

The preferred form of repeater, Figs. 1 and 3, is referred to as RI. The modified form of repeater oi Figs. 2 and 4, is referred to as R2, and the further modiiied forms of Figs. 5 and 6 are ,referred to as R3 and R4.

PREFERRED EMBODIMENT; FIGURES 1 AND 3 Referring iirst to the repeater RI of Figs. 1 and 3, this repeater is interposed between two sections LW and LE of a two-way telephone line (usually a long-distance line or trunk). Section LW is coupled to conductor 42| of the repeater by way of repeating coil ll, and section LE of the line is coupled to conductor I4! of the repeater by way of repeating coil |03.

Balance networks BW and llily (sometimes referred to as artificial lines) are associated respectively with line sections LW and LE. Each such section may comprise the usual impedance elements arranged in the usual manner to provide substantially an electrical equivalent of its associated line section.

Referring now particularly to Fig. 3, voice currents arriving over line section LW reach conductor I2I through repeating coil Itl, and pass through amplifier IA, conductor |28 and amplifier IUBA to reach conductor UH, whence they reach line section LE by way of repeating coil |03. Similarly, voice currents arriving over line section LE' are amplified and repeated to line section LW by passing through repeating coil |03 to reach conductor |4I, whence they pass through amplifier |08A, conductor IiS, and ampliiier I05A to conductor |2|, thence to line section LW by way of repeating coil IIii.

The remaining parts of repeater Rl are those concerned with preventing feed-back, or singing, between the two oppositely directed amplifying channels represented by conductors |40 and |20 respectively. The arrangement for preventing amplified voice currents from` returning (feeding back) from conductor |41 to conductor iii, incident to their passage from section LW to section LE, includes balance network BEl repeating coil |04 and associated parts |0'IB, liB, |0813, and conductor i4 l. Part |0'IB is a phase inverter, such as vacuum-tube amplifier adjusted for aero amplication, while parts |B and |0023 are amplifiers similar respectively to ampliners |05A and |08A.

When voice currents pass over conductor |20 toward line section LE', by way or amplier |09A and conductor IM, such voice currents pass also through phase inverter |0'IB and thence through amplifier |003, to reach conductor I4I in direct phase opposition to the voice currents reaching conductor mi. The voice currents passing over conductor IllI to reach line section LE are modified in accordance with the electrical character istics of such line section. On the other hand, the voice currents passing over conductor iM to reach the associated balance network BE` are similarly modified, with the result that the voice currents on conductors |4| and I-tl' may be exactly similar except that they are in direct phase opposition by virtue of the action of phase inverter |07B. Consequently, the amplified voice currents passing to return conductor M8 from conductor Elli, by way of amplier |08A, are exactly neutralized by the similar, out-of-phase voice currents passing from conductor IM' through ampliner NSB to conductor 5&3. Consequently, the net effect on conductor idd is zero when all the concerned parts are in balance.

A similar arrangement prevents outgoing voice currents traversing conductor I2I, on their Way to line section LW, from feeding back over conductor |28 to conductor I4|. t includes phase inverter IEVIA, amplifiers WEB and WEB, conductor 12|', repeating coil |02, and balance network BW, associates1 with line section LW.

At this point it may be noted that an exact balance is not required, and that it is permissible for a certain amount of voice currents to be returned over either of the conductors |48 and |28, so long as such returned voice currents are of a power substantially lower than the initial voice currents, whereby local oscillation (singing) is avoided. The considerations in this respect are similar to those surrounding two-way telephone repeaters of the prior art. The required degree of balance against intolerable amounts of returned energy is generally in proportion to the amount of gain required through a channel of the repeater. General considerations usually limit the allowable gain to about ten decibels, which represents a maximum increase in power through an amplifying channel of 10 to l, or a voltage increase of slightly in excess of 3 to l.

Referring now to Fig. l, it shows a suitable circuit arrangement for carrying out the previously described arrangement shown in blockdiagram form in Fig. 3. The amplifiers and phase inverters of Fig. 3 appear in Fig. l as ve double-triode vacuum tubes |05 to |09. rEhe two triodes of any such tube are separately identified as parts A and B thereof. For example, ampliiiers I05A and |05B of Fig. 3 include respectively parts A and B of double triode tube I of Fig. 1.

Each of the triodes of Fig. l includes a grounded cathode indirectly heated by the indicated heating element. The circuit arrangement for the heaters is not shown as it forms no part of the invention. The circuit arrangement of Fig. l further requires a grounded source of positive potential for the plates (anodes) of the triodes, and a grounded source of negative potential for biasing the grids (control electrodes) of the triodes to the desired point. These two grounded sources are not shown, but the connections to them are indicated by terminals inarlred accord ing to the polarity of the source.

Plate current is supplied to the two triodes of tubes |05 and |09 through the local windings of repeating coils i0| to |04. Plate current is supplied to the two triodes ci tube les through common resistor liz, and to the two triodes oi' tube |00 through similar resistor iii. Plate our rent is supplied to triodes A and B o phase inverter tube |01 through resistors ist and 20.

Biasing potential is supplied to the two triodes of tube |05 through grid resistors itil and'to tube |08 through similar resistors Biasing potential is supplied to triode B of tube i0? and to trode A of tube |09 by way ci the slide arm of potentiometer |21 and conductor It, potentiometer |21 being employed as a gain-oontrol device through which the gain in signals passing from section LW to section LE is adjusted. Biasing po tential is similarly supplied to section A of tubes |05 and |01 through the slide arm of gain-control potentiometer Ili and conductor lat, device isi being adjustable according to the gain desired in signals passing from section LE to section LW.

Biasing potential is supplied to triodes B of tubes |05 and |09 through the slide arms of potentometers I5| and I3| respectively. Such potentiometers are adjustable to secure the desired state of zero amplication through each of the triodes A and B of phase-inverter tube E0?.

The plates of tube |05 are connected respectively to the grids of tube |00 through coupling condensers |22; coupling ccndensers iii? serve similarly between tubes it@ and itt'. Coupling condenser |26 is located between the plates oi tube |06 and gain-control potentiometer l2?. Condenser |46 is similarly interconnected between tube |08 and potentiometer ifi?. Condensers |30 and |50 interconnect sections B and A of phase-inverter tube |01 respectively with potentiometers |3| and |5I.

Signals arriving on conductor i2! from line section LW traverse the associated condenser |22 and conductor |23 to reach triode A of tube |00, passing thence by way of potentiometer iii?, to conductor |28. From conductor E25, euch signals pass through tricde A of tube los to reach conductor IM, whence they pass through repeating coil |03 to line section LE. The signals on conductor |28 also pass through triode B of phase-inverter tube |01, passing thence through condenser |30, potentiometer |3|, triode B of tube |09, whence they reach balance network BE. by way oi repeating coil |041. Having passed through phase-inverter triode B of tube |01, the signals on conductor Il' are in direct phase opposition to those on conductor |4|. Signals from these two conductors proceed through condensers i42 and conductors |43 through both triodes of tube 08. The plate current variations in either triode of tube |08 are accordingly exactly offset by plate current variations in the other triode thereof, whereby no net change in plate current results. Accordingly, no return signal passes through condenser |45 to conductor |48.

Similarly, signals arriving on conductor |4| from line section LE reach triode A of tube |08 through the associated condenser |42 and conductor |43, passing thence through condenser |46, gain-control potentiometer |41, conductor |48, triode A of tube |05, to conductor |2|, passing thence to line section LW by way of repeating coil lThe signals on conductor |48 also reach conductor i2 I by way of triode A of phaseinverter tube |01, condenser |50, potentiometer |I, and triode B of tube |05, thence reaching balance network BW by way ci repeating coil |02. The signals on conductor |2I are in direct phase opposition to those on conductor |2I, with the result that equal and opposing signals are impressed through condensers |22 and conductors 12s on the grids of sections A and B of tube |05, resulting in no net change in plate current of that tube, wherefore no resulting return signal reaches conductor |23.

It may be noted that potentiometer |3|, for example, while provided primarily to adjust the associated triode B of phase-inverter tube |01 to zero amplification, this potentiometer is not necessarily adjusted to the exact zero-gain point in the event that the two triodes of tube |09 possess slightly unequal amplifying properties. Potentiometer |3| is adjusted in any event to cause the opposed potentials appearing on conductors |4| and |4| to be equal, except that they may be slightly unequal to further compensate or any amplifying unequality which exists between the two elements of tube |08. It is clear therefore that potentiometer |3| should be adjusted to give the same gain through triodes B of tubes |01, |00, and |08 as is realized through triodes A of tubes |09 and |08. Similarly, potentimeter should be adjusted to provide the same gain through triode A of tube |01 and triodes B of tubes |05 and |00 as is realized i through triodes A of tubes |05 and |00.

In Figs. 1 and 3, with phase inverters |01B and |01A located respectively between conductor |28 and the input of amplier lB, and between conductor |40 and 'the input of amplifier |05B, the potentials applied by the repeater to conductors |4| and |4|' are out of phase with each other, as are the potentials applied by the repeater to conductors |2| and |2|. Consequently, an increase in current flow through the local Winding of repeating coil |03 is accompanied by a corresponding decrease in current now through the local winding of repeating coil |04. The same condition exists with respect to the local wind-` ings of repeating coils |0| and |02. Accordingly, the arrangement of Figs. 1 and 3 is such as to cause a minimum of change in plate current incident to operation, 'reducing the tendency for cross talk between repeaters incident to poor voltage regulation of a common source of platecurrent supply.

The nature of the repeater arrangement being described is such that either line section is interchangeable with its associated balance network. For example, line section LW may be attached to the terminals of the line winding of repeating coil |02, and balance network BW may be attached to the terminals of line winding of repeating coil I0 If such a transposition is made, signals impressed on conductor |48 from line section LE reach line section LW by way of element A or tube |01 and element B or" tube |05 directly out of phase with equal signals reaching balance network BW by way of element A of tube |05. Also, with this transposition made, signals arriving over section LW pass through repeating coil |02 to reach conductor |2|, whence they pass by way of section E of tube |06 to reach conductor |28 on their way toward line section LE.

SECO-ND EMBODIMENT; FIGURE-S 2 AND 4 Repeater R2 of Figs. 2 and 4 is similar to repeater RI of Figs. 1 and 3, except that the phase inverters occupy a different position within the latter arrangement.

In-phase signals are impressed on conductors 22| and 22|', and on conductors 2M and 24|', in that phase inverters 201A and 201B are located beyond conductors 24| and 22|'. These phase inverters are located respectively between such conductors and the input of amplifiers '208B and 206B. Accordingly, the in-phase currents are changed to out-of-phase currents in the output circuits of the pairs of ampliers comprising 206A and 200B, and 208A and 200B. The net result is that signals repeated to conductor 20| by the repeater R2 are prevented from returning over conductor 2:18, and signals repeated by the repeater to conductor 22| are prevented from returning to conductor 220, but alterations in current flow over conductor 22| are accompanied by similar in-phase alterations of similar flow over conductor 22|', the same exisitng with respect to conductors 24| and 24|. Accordingly, a better voltage regulation of a common power supply is required with the arrangement of Figs. 2 and 4 than is required with the arrangement of Figs. 1 and 3.

Referring now particularly to the circuit diagram of the repeater R2 as shown in Fig. 2, line sections LW and LE correspond respectively to line sections LW and LE associated with the repeater R|; balance networks BW and BE correspond respectively to balance networks BW and BE; repeating coils 20| to 204 correspond respectively to repeating coils |0| to |04; and tubes ses to 209 correspond respectively to tubes |00 to |03. The remaining elements of Fig. 2 correspond to elements of Fig. 1, each such element having applied thereto a reference numeral beginning with the digit 2 rather than with the digit It will be noted that signals incoming -from line sections LW' pass by way of conductor 22 l, triode A of tube 206, conductor 228, and potentiometer 221 to the two grids, in parallel, of triodes A and B of output tube 205, causing equal in-phase currents to flow in conductors 24| and 24|. The signals represented by these conductors are accordingly transmitted equally to line section LE and to its associated balance network BE. Such signals also pass through condensers 2:12 and conductors 243 to reach triodes A and B of tube 208. The signals from conductor 24| reach triode A of this tube directly, while the signals from conductor 24| reach triode B of tube 200 through triode B of phase inverter tube 201, whereby the resulting plate-current change in triode B is directly out of phase with that in triode A of tube 208. Potentiometer 23|, located between conductor 24|' and the input of phase-inverter triode B of tube 201 is so adjusted that the out-ofphase plate currents in triodes A and B of tube 203 are equal, whereby no resulting return signal reaches conductor 248.

The signals incoming from line section LEI' to conductor 24| pass similarly over conductor 248 to reach line section LW by way of conductor 22|, accompanied by equal signals on conductor 22|. The latter signals having their phase inverted through section A of tube 201 to reach section B of tube 206 directly out of phase with the signals reaching section A of this tube from conductor 22 I, whereby no resulting signal is fed back to conductor 228.

THIRD EMBODIMENT; FIGURE 5 The third embodiment of the invention, repeater R3 of Fig. 5, is similar to the first embodiment except that amplifiers |06A and |05B have been replaced by center-tapped resistor 5in, and ampliiiers IDEA and |08B have been replaced by the similar resistor 580. Each such resistor may be provided with a xed center tap, or a slide-arm connection may be employed, as indicated, to permit adjustment to the point of minimum feed-back.

Incoming signals reaching conductor 52|, by way of repeating coil 50|, pass through the upper section of resistor 510, coupling condenser 526, and gain-control device 521, to reach conductor 528. From this point, such signals divide, one portion passing through amplifier 509A to reach conductor 54|, associated with the outgoing line section, the other portion passing through phase inverter 5MB and amplifier 5MB to reach conductor 54| associated with the outgoing balance network. Such signals accordingly reach conductors 54| and 54| in direct phase opposition, applying equal and opposite potentials to the two terminals of resistor 539, Being connected to the mid point of resistor 5&5, conductor 548 is unaffected by these potentials, wherefore return feed-back of the outgoing signal is prevented.

Similarly, incoming signals arriving on conductor 54| by way of repeating coil 503, pass through the upper section of resistor 580, coupling condenser 545, and gain-control device 541, to reach conductor 548. Such signals pass toward the opposite line section through amplifier 505A and conductor 52|, at the same time proceeding toward the associated balance network by way of phase inverter 501A, amplier 505B, and conductor 52|. The equal and opposite potential variations on conductors 52| and 52| cause a current to ilow through both sections of resistor Elli, but conductor E22 remains unaffected because connected to the center point of the resistor.

The arrangement of Fig. 5 is particularly useful where the gross grain required in either direction can be supplied by a single amplifier 505A or 50th, keeping in mind that the signal suffers a loss in potential on the order of one-half in the passing through a center-tapped resistor 510 or 532.

FOURTH EMBGDIMENT; FIGURE 6 The fourth embodimentof the invention, re-

8 peater R4 of Fig. 6, is similar to the third ernbodiment shown in Fig. 5 except that ampliers 51| and 68| are inserted in conductors 528 and EGB respectively. The arrangement of Fig. 5 is thus inodiiied to provide two tandem-related stages of amplification for each direction of signal transmission, permitting simple triode tubes to be employed to obtain any net gain through the repeater likely to be required. It will be noted that condenser 525 and gain control potentiometer 52? are not separately7 shown in Fig. 6. They may be considered as incorporated Within amplification stage 6i The sample applies to the oppositely directed amplication stage 68|.

With respect to any of the disclosed repeaters Rl to R4, if desired, one of the balance networks associated therewith may be omitted, along with its associated phase inverter and amplifying apparatus, without rendering the repeater liable to sing or howL provided a particularly exact balance obtains between the remaining balance network and its associated line section, and between the channel branch containing the remaining phase inverter and the opposed channel branch. For example, considering repeater RI as shown in Fig. 3, balancing network BW may be omitted, along with repeating coil |02, phase inverter IMA, and amplifiers iiB and IlB. With this removal accomplished, signals arriving over line section LW proceed as before over conductcr |2I, through amplifier |05A, and thence over conductor |23 to reach conductors |4| and |4| in direct phase opposition, whereby the amplined signals transmitted to section LE are prevented from returning over conductor |48 to the originating line section as previously described. On the other hand, signals arriving over line section LE' and traversing conductors |4| and |48 to reach conductor |2| (amplied by amplifiers WBA and IBSA), pass to section LW as before, but are returned, through amplifier IliA to conductor |28, whence they reach conductor |4| by way of amplifier 629A, considerably amplified with respect to their initial passage over conductor |4|. The returning signals also pass from conductor |28, through phase inverter |01B, and amplier IGQB, reach conductor |4| directly out of phase with their appearance on conductor I4 I, and equally ampliiied. These greatly amplified, returned signals pass through amplifiers IBSA and |0813 to reach conductor |48 as equal and opposed potentials, wherefore they are mutually canceled at that point to prevent further propogation thereof. The foregoing abbreviated arrangement, while not recommended for most purposes, may nevertheless be of utility under certain circumstances.

I claim:

1. ln a two-way telephone repeater for interconnecting a rst section and a second section of a two-way telephone line, a balance network associated with said second section, circuit apparatus providing a nrst amplifying channel for transmitting amplified signals from the first seotion to the second section, and providing a second amplifying channel for transmitting amplified signals from the second section to the rst, the iirst channel having a pair of output branches leading therefrom respectively to the second line section and its associated balance network, the second channel having a pair of input branches leading thereto respectively from the second line section and its associated balance network, the second line section and its balance network each providinga junction for an output branch of one channel and an input branch of the other channel, and a phase inverter serially related to one of said. four branches.

2. In a two-way telephone repeater for interconnecting two sections of a two-Way telephone line, balance networks associated with said line sections respectively, circuit apparatus providing two oppositely directed amplifying channels for transmitting ampliiied signals between the sections, each channel having a pair of similar input branches leading thereto respectively from a line section and from its associated balance net- Work, each channel having a pair similar output branches leading therefrom respectively to the other line section and to its associated balance network, each line section, and each balance network, thus providing a junction for an output branch of one channel and an input branch of the other channel, and means for inverting the phase of the signals traversing one of the four said branches associated with each line section with respect to the signals in the other branch of its said pair to prevent local signal circulation through the two channels serially.

3. A two-way amplier system comprising two bridge networks, each network consisting of two impedance elements in adjacent arms and two ampliiier tubes in the other two arms of the bridge, a signal input circuit asymmetrically connected across one diagonal defined by the junction points of each element and a tube, and a signal output circuit asymmetrically connected across the other diagonal and to the input of one amplier tube of the second network.

4. A two-way amplier comprising a first and a second Wheatstone bridge, each bridge having an amplifying tube in each of two adjacent arms and balancing impedance elements in the remaining arms, a two-Way signal circuit coupled across the diagonal of each bridge defined by the apices between the tubes and impedance elements, the other diagonal of each bridge being coupled across the input of one tube of the opposite bridge.

5. In the two-way amplifier dened in claim 4, each of said two-Way signal circuits positioned asymmetrically in the coupled diagonal with respect to the electrical center of the diagonal.

6. In the two-way amplifier deiined in claim 4,

each of the first mentioned diagonals including the Winding of a signal transformer and a series impedance element, the junction of the winding and the series element being fixed at a grounding potential with respect to the remainder of the bridge.

7. In combination, four impedance arms connected together to form a four-terminal bridge and an unbalanced-toeground, two-way wave transmission circuit, an unbalanced-toeground input circuit, an impedance approximately matching the impedance of said transmission. circuit, and an unbalanced-to-yround output circuit connected, respectively, to the terminals of said bridge in the order recited, one of said arms including means for reversing the phase of the current therein.

8. The combination in accordance with claim 7 in which said phase-reversing means comprise an amplifier.

9. The combination in accordance with claim 3 in which said one arm includes a blocking capacitor connected in series with said amplifier.

10. In combination, ,fo-ur impedance arms connected together to form a four-terminal bridge and an unbalanced-to-ground, two-way wave transmission circuit, an unbalanced-to-ground input circuit, a balancing network for said transmission circuit and an unbalanced-to-ground output circuit connected, respectively, to the terminals of said bridge in the order recited, one of said arms including means for reversing the phase of the current therein.

11. The combination in accordance with claim 10 in which said phase-reversing means comprise an amplifier.

12. The combination in accordance with claim 11 in which said one arm includes a blocking capacitor connected in series with said amplifier.

13. The combination in accordance with claim 10 in which said one arm is connected between said input circuit and said balancing network.

References Cited in the 111e 0f this patent or the original patent UNITED STATES PATENTS Number Name Date 1,353,637 Crisson Sept. 21, 1920 2,002,499 Black May 28, 1935 2,004,598 Bjornson 1 June 11, 1935 2,106,337 Black Jan. 25, 1938 2,229,806 Holzler Jan. 28, 1941 2,258,275 Black n Oct. 7, 1941 FOREIGN PATENTS Number Country Date 501,234 Great Britain Feb. 23, 1939 103,041 Sweden Sept. 18, 1941 

